Radio terminals, such as portable telephones, PHS (personal handyphone system), or small-size personal computers provided with a telephone or data communication function, have become popular. These radio terminals have been extensively used for calls, as well as for electronic mails or communication of various data. Further, this radio data communication environment has also become used to distribute pay data. Distribution of data by a distribution server is disclosed, for example, in Japanese Patent Laid-Open Nos. 184087/2000, 269078/1998, and 096237/1999.
Since acquisitors or users pay a charge for pay data, a premise is that data per se have an economical value. Such data include, for example, certain image data, musical piece data, text data, and program data, for example, for video games. Up to now, users have acquired most of these data in the form of records comprising the data recorded in recording media, such as paper or CDs (compact disks), by mail or through sales in shops. As described above, however, the advance of communication environment has made it sufficiently possible to realize a commercially acceptable system wherein, for example, the radio data communication environment is utilized to acquire these data as pay data. Delivery of the above pay data to users through the utilization of the radio data communication environment involves problems of reliable data distribution and accounting with respect to the equivalent to the data.
A large number of proposals have hitherto been made on data distribution systems for pay data distribution and accounting. These proposals can be roughly classified into two basic types. The first type is such that pay data are encrypted and, upon the payment of an equivalent to the data, a user receives key data. The second type is such that the right of access to pay data is authorized only to users who have previously paid the equivalent.
These proposals, however, are on the assumption that the distribution side of pay data is connected to users through a wired communication line, In wired data communication environment, the lowering of communication expense is being extensively carried out, and, in addition, the environment of leased lines or full-time connection is being prepared. Further, in many cases, data transfer rate per unit time is much higher than that in radio communication.
On the other hand, in the case of radio data communication environment, the data transfer rate is in many cases lower than that in the case of the wired data communication environment, and, in addition, the communication charge is high. For this reason, at the present time, systems for the distribution of pay data, which has been performed through communication equipment using wired transmission lines, such as telephone lines or CATV (cable television), are difficult to be spread in the field of radio data communication. Problems involved in the radio data communication environment will be explained in more detail.
The first problem is that the time period between the start of the user's operation for the acquisition of pay data and the acquisition of the contemplated data followed by reproduction or utilization of the data is long. The conventional first type of data distribution systems, wherein pay data are sent and are deciphered using a key, is on the assumption that a considerable quantity of initially encrypted pay data as one unit is entirely sent to the user side. This is because the data cannot be properly decrypted so far as at least one unit of encrypted data is not present on the user side.
For example, regarding general pay data, in the case of the acquisition of data on one piece of music, the size of one pay data is about 2 M (mega) bytes to about 3 M bytes. When this pay data is acquired through data communication, for example, by means of PHS of 64 K (kilo) bits/sec, the time necessary for this is about 10 min. In this case, in addition to the time necessary for the download, the procedure for the issue of a key and the communication time for the transmission of the key are further necessary.
Also in the second type system wherein the right of access to the pay data is authorized only to users who have previously paid the equivalent, the time period between the start of the operation for the acquisition of pay data and the completion of acquisition of the pay data is the same as that required in the first type system because the communication environment is identical. That is, for both the systems, since the data transfer rate is so low that a considerably lot of transfer time is required for acquiring one data on average, and, thus, when the communication time is the basis of the charge, the communication charge is increased by the extra time. On the other hand, when the data quantity is the basis of the charge, the probability of the occurrence of communication error increases with increasing the communication time. This often poses a problem that the reliability of the receipt of data is lowered.
The second problem involved in the radio data communication environment is that, in relationship with the start time of the distribution of pay data, the distribution processing of the distribution server is likely to be concentrated. Therefore, the distribution server should have a performance high enough to withstand the high load which temporarily occurs. To cope with the temporary high load, an excessive performance and an equipment cost for obtaining this performance are required as compared with the case where, for example, the load on the distribution server has been equally dispersed.
When the distribution server does not have satisfactory performance, it is a matter of course that the time period between the user's request for the distribution of pay data and the completion of the distribution of the pay data is sometimes significantly increased. For example, on the date of sale or at the time of sale of musical piece data or game programs, the request for the transmission of pay data is likely to be intensively made from each terminal of users. For example, in the case of the musical pieces, data of 2 M bytes to 3 M bytes for each request should be continuously sent by the distribution server to the user who has requested the transmission of data. When processing of send data beyond the number of communication lines connected to the distribution server or beyond the bandwidth of the communication path is necessary, however, the processing for each user is delayed and, thus, the data distribution processing per se is delayed.